SEOUL, South Korea >> South Korea fired dozens of shells Thursday at rival North Korea after the North lobbed a single rocket round at a South Korean town near the world’s most heavily armed border, the South’s Defense Ministry said.

The Defense Ministry said in a statement that its artillery shells landed at the place where North Korea had fired its rocket. There were no other immediate details from the military and no reports of injuries. It appeared that North Korea did not respond to South Korea’s returned fire.

North Korea had previously threatened to attack South Korean loudspeakers that have been broadcasting, for the first time in 11 years, anti-Pyongyang propaganda messages across their shared border. Pyongyang also restarted its own loudspeakers aimed at the South.

About 80 residents in the South Korean town where the shell fell, Yeoncheon, were evacuated to underground bunkers, and authorities urged other residents to evacuate, a Yeoncheon official said, requesting anonymity because he wasn’t authorized to speak to the media.

In the nearby border city of Paju, residents were asked to stay home. On Baeknyeong Island near the Koreas’ disputed western sea boundary — the scene of several bloody skirmishes in recent years — residents in villages near a site where South Korea operates one of its loudspeakers were also evacuated, according to island officials.

The cross-border propaganda warfare followed accusations from Seoul that Pyongyang had planted land mines on the South Korean side of the Demilitarized Zone that maimed two South Korean soldiers earlier this month. Pyongyang has claimed that Seoul fabricated the evidence on the land mines and demanded video proof.

Authoritarian North Korea is extremely sensitive to any criticism of the government run by leader Kim Jong Un, whose family has ruled since the country was founded in 1948.

Last October, North Korean troops opened fire at areas near Yeoncheon, after South Korean activists launched balloons there that carried propaganda leaflets across the border. South Korea returned fire, but no casualties were reported. Later in October, border guards from the two Koreas again exchanged gunfire along the border, without any casualties.

Before that, the Koreas tangled in a deadly artillery exchange in 2010, when North Korean artillery strikes on a South Korean border island killed four South Koreans. Earlier in 2010, an alleged North Korean torpedo attack killed 46 South Korean sailors.

North Korea’s army said recently in a statement that the South Korean propaganda broadcasts were a declaration of war and that if they were not immediately stopped "an all-out military action of justice" would ensue.

South Korean President Park Geun-hye urged Pyongyang to "wake up" from the delusion that it could maintain its government with provocation and threats.

Thursday’s artillery exchange came four days after South Korea and the United States began annual summertime military drills that North Korea calls an invasion rehearsal. Seoul and Washington say the drills are defensive in nature.

South Korea has said the two soldiers wounded from the mine explosions were on a routine patrol in the southern part of the DMZ that separates the two Koreas. One soldier lost both legs and the other one leg.

The Koreas’ mine-strewn DMZ is a legacy of the 1950-53 Korean War, which ended with an armistice, not a peace treaty.